Process and device for surface-modification by physico-chemical reactions of gases or vapors on surfaces, using highly-charged ions

ABSTRACT

The invention concerns a process and a device for surface-modification by physico-chemical reactions with the following steps: a) contacting a solid surface having a crystalline or amorphous structure with a reactive, gaseous fluid (gas, gas mixture, vapour or vapour mixture) which is to interact with the surface; (b) supplying activating energy to the contact area between fluid and surface by means of ions or plasmas, in order to trigger reactions between said partners. In order to improve such a process and device, the activating energy is supplied as ions having at least a double charge and low kinetic energy or plasma streams with a sufficient proportion of ions having at least a double charge and low kinetic energy. The kinetic energy imparted to the ions is selected so that it allows the ions to closely approach the surface atoms but no to enter the surface.

BACKGROUND OF THE INVENTION

The invention concerns a process for surface-modification byphysico-chemical reactions with the steps:

(a) contacting a solid surface having a crystalline or amorphousstructure with a reactive, gaseous fluid (gas, gas mixture, vapor orvapor mixture) which is to interact with the surface,

(b) supplying activating energy to the contact area between fluid andsurface by means of ions or plasmas, in order to trigger reactionsbetween said partners,

as well as a device for the implementation of the process.

The process therefore includes for instance the coating or etching ofsurfaces by physicochemical reactions of reactive, gaseous fluids(gases, gas mixtures, vapors or vapor mixtures) at the surfaces,supported by plasmas or ion beams, which

(a) deposit coatings on the surface by the interaction of the gases, gasmixtures or vapors at a surface with ion beams or a plasma, which arecomposed of radicals of said gases or vapors, or

(b) erode (etch) surface atoms by the interaction of the reactive fluidsat the surface with ion beams or with a plasma by forming volatilemolecules from surface atoms and radicals of the said gases or vapors,or

(c) desorb, and so erode or etch, respectively, surface atoms or-molecules by the interaction of the ions at the surface.

It is known, that processes employing ion beams and plasmas in thepresence of gases or vapors, depending on the choice of these gases orvapors, are used for the etching of surfaces, or the coating ofsurfaces, or for the production of thin films on surfaces. A summary ofthe foundations and of the technical state of the art of these processesis found in three publications:

I. R. A. Haefer, "Oberflachen- und Dunnschicht-Technologie" ("Surfaceand Thin Film Technology") Part 2; "Oberflachenomodifikation durchTeilchen und Quanten" ("Surface Modification by Particles and Quanta")Series Werkstoff-Forschung und Technik (Materials Research andTechnology), Volume 6, Springer 1991;

II: "Low Energy Ion Beam and Plasma Modification of Materials", eds. J.M. E. Harper, K. Miyake, J. R. McNeil, and S. M. Gorbatkin, SymposiumProceedings of the Materials Research Society, Vol. 223, MaterialsResearch Society, Pittsburgh, USA, 1991;

III: Comptes Rendus des Travaux du "8eme Colloque International sur lesProcedes Plasma" (Contributions to the "8th International Colloquium onPlasma Processes"), Le Vide les Couches Minces, Supplement 256, 1991,

referred to as I, II, and III, respectively.

Subsumed to the term "Surface-Modification" have to be particularlysurface-coating and surface-etching.

For the coating of surfaces from gases or vapors, energy has to belocally supplied at the surface for the physico-chemical reaction of thegases or vapors to create bonding with the surface, in order to obtainthe coating of the surface with the desired compound. That is whythermal energy supply allows for instance to produce Si₃ N₄ -coatings onSiO₂ -films by streaming gases of SiH₄ and N₂ against surfaces of SiO₂-films heated to high temperatures (>600° C.). Such processes are called"Chemical Vapor Deposition", CVD. For many applications the CVD-processfaces, however, the disadvantage to work only at high temperatures.

It is known, published application of the German Patent Office DE4020816 A1, referred to as D1 in the following, to improve theCVD-process by special devices for the transport of reactants towardsthe surface, in order to obtain coatings with higher purity. To thatend, in D1 for instance, substances are activated (ionized) by variousmethods and accelerated, then electromagnetically separated, and thendecelerated and neutralized before they react at the surface to form acoating.

It is known, to work at reduced surface temperatures by supplying theenergy for the physico-chemical reaction at the surface by impingingsingly charged ions with kinetic energy. The ions may stem from a plasmaor from an especially prepared ion beam.

In the case of a convectional plasma, one speaks of "Plasma Enhanced (orActivated) Chemical Vapor Deposition", PECVD or PACVD. With it oneobtains a reduction of the surface temperature for the Si₃ N₄ -coating,described above, to about 300° C. With the more recent "ElectronCyclotron Resonance", ECR-plasmas, this temperature can be furtherreduced to about 150° C. One speaks then of ECR-PECVD, which is appliedalready, but is still subject of research for all its possibleapplications. On the progress with ECR-PECVD on the production ofdiamond coatings from the gas mixture of CH₄ and H₂ has been reported[F. Roy, M. Mermoux, B Marcus, III, pages 353 to 355].

The replacement of the plasma by an ion beam with single charge andenergy allows a still better localization and concentration of theenergy supplied for the CVD at or on the surface of the substrate and soallows a further reduction of the temperature of the substrate. Thisenergy is mainly supplied by the absorption of the kinetic energy of theions in the first surface layers in the form of a surface activation.One speaks therefore of "Ion Activated CVD", IACVD. This IACVD is ofparticular interest, since gases or gas mixtures which adsorb at thesurface are activated together with the surface only by the ionbombardment and the resulting solid compounds are deposited as films.This technology yields good coating results especially at lowtemperatures (i.e. -100° C.) of the substrates [M. Hirose, H. Shin, S.Miyazaki, and Y. Hriike, III, pages 105 to 112]. The type of ion is atfree choice, so that ions of the coating to be deposited can be used,which yields coatings with higher purity. By using low energy C⁺ -ionsfor instance, diamond crystal coatings with high purity could beproduced [J. W. Rabalais and S. Kasi, Science 239, (1988), page 623].The tribologically important transition metal-nitride or -carbidecoatings can also be well produced by using N⁺ - or C⁺ -ions.

For the surface etching with gaseous reactive fluids (gases or vapors),energy has to be locally supplied at the surface for thephysico-chemical reaction of the gases or vapors with the surface. Thisenergy mainly serves to liberate reactive radicals from the gasmolecules which form together with the surface atoms volatile moleculesand do so erode the surface. On hot Silicon surfaces, for instance, veryreactive, neutral fluorine atoms are separated from CF₄(tetrafluoromethane) which form volatile SiF₄ at the Si-surface and doso erode the Si-surface on a large scale.

When the dissociation is energetically supported by a plasma, forinstance, reactive ions are also formed which serve for an increasedetching of the surface. In the preceding example, CF₃ ⁺ -ions add to theetching besides the neutral fluorine atoms. In this case one speaks of"Reactive Ion Etching", RIE. The ions may have kinetic energies up tosome 100 eV and do so not only dissociate the gas molecules, but causealso a physicochemical activation of the surface atoms. Since thisactivation depends on the direction of impact of the ions, spatiallydirected etching can be achieved in particular when the ion productionis spatially separated from the region of the substrate. A directed ionbeam can then interact with the substrate; the etching gas streamssimultaneously towards the substrate. One then speaks of "Reactive IonBeam Etching", RIBE. As examples may serve the etching of Al₂ O₃ or Auby Cl⁺ ions supported by simultaneous streams of CCl₄ or C₂ F₄ Cl₂ [I,chapter 7.6, pages 205 to 217].

It is an advantage of the RIBE-process that the gases or gas mixtureswhich adsorb on the surface are activated together with the surface onlyby the ion bombardment, combine with molecules (atoms) from thesubstrate and do so allow a well controlled etching of the surface. Thistechnology yields precise etching results especially at low temperatures(e.g. -100° C.), where the gases or gas mixtures are well adsorbed [M.Hirose. H. Shin, S. Miyazaki, and Y. Horiike, III, pages 105 to 112; R.Petri, J. -M. Francou, D. Henry, and A. Inard, III, pages 94 to 97].

In these ion assisted coating- or etching processes ion bombardment isdisadvantageous that the kinetic energy of the ions, which is necessaryfor the creation of the local surface activation or for the localphysico-chemical activation, is so high that a damage of the materialbeneath the surface and of the coating already deposited can not beavoided. These material defects have important consequences. Experimentshave shown that electronic or opto-electronic components produced withthese processes had too high a density of defects and could thereforenot be used. Long lasting annealing processes had to be appliedtherefore, which ruined the technological advantages of the productionprocess [D. Lootens, P. Clauws, P. Van Daele, and P. Demeester, III,pages 292 to 294].

SUMMARY OF THE INVENTION

A principal object of the invention is, to improve the aforementionedprocesses in order to avoid the damage of the material to be modifiedbeneath its surface and of the coatings already deposited. The timeconsumption for the annealing of these defects could thus be reduced andthe productivity could thus be considerably improved.

This object, as well as other objects which will become apparent in thediscussion that follows, is achieved, in accordance with the presentinvention, by supplying the activating energy as ions having at least adouble charge and low kinetic energy or plasma streams with a sufficientproportion of ions having at least a double charge and low kineticenergy. The kinetic energy imparted to the ions is selected so that itallows the ions to closely approach the surface atoms but not to enterthe surface.

In other terms, the surface of the material to be treated is bombardedwith ions having at least double charge and low kinetic energy, wherethe potential energy of the ions, corresponding to their high charge, isused for activating the surface, the gas molecules adsorbed at thesurface, or the gas molecules just in front of the surface. The ions canapproach the surface atoms but can not penetrate the surface.

As mentioned already, surface modification is understood to representparticularly etching, coating or depositing. The coating or etching ofsurfaces is obtained by the interaction of highly charged ions with lowkinetic energy with the surface, with the gases or vapors adsorbed atthe surface, or with the gas molecules just in front of the surface.Contrary to the use of the relatively high kinetic energy for thephysico-chemical activation in the known RIE-, RIBE, PECVD-, orIACVD-processes, it is the potential energy stored in the highly chargedion which is used for the coating and etching of the surfaces. Therelatively low kinetic energy of the highly charged ions is onlynecessary to closely approach the surface atoms or molecules to beactivated. The electronic interaction of highly charged ions with asurface has on the one hand side an influence on the electronic state ofthe ion by electron exchange between the surface and the ion, and on theother hand on the trajectory of the ion by the attractive force of theimage charge, which, for the case of electrically conducting surfaces,is equal to the effective charge of the ion in front of the surface. Atelectrically non conducting surfaces this force is strongly reduced andcan become zero. The electron exchange from the material's surfacetowards the highly charged, incoming ion sets in, in terms of atomicunits of length a₀ =0.0529 nm, at great distances z_(c) in front of thefirst atomic layer of the surface, which is assumed to be located atz=0.

It is of significance for the invention that the highly charged ion, onits further path from z_(c) to a distance z=d in front of the firstatomic layer, resonantly captures electrons from the surface into highlyexcited states, and so reduces its initial charge, or becomesneutralized in front of conducting surfaces, respectively, where d isthe average lattice distance between atoms in the surface plane. Sincethese electrons stem from the conduction or valence band of the surfacematerial, respectively, or from valence electrons of adsorbed atoms ormolecules, the resonance energy is determined by the binding energy ofthese bands or of these valence electrons.

By this "aspiration" of (valence-) electrons from the surface localbondings of adsorbed atoms or molecules will be strongly reduced so thatthey become physico-chemically activated (excited). By this activationatoms or radicals of the adsorbed molecules can form new bondings andcan so produce a coating of the surface, or, depending on the choice ofthe adsorbed atoms or molecules, can create with surface atoms volatilemolecules and can so erode (etch) the surface, well before the incoming,initially highly charged ion arrives at the close vicinity (Z<d) of thesurface atoms. At semi-conducting up to non-conducting, clean surfacesthis "aspiration" of valence electrons can directly produceCoulom-desorption, i.e. erosion (etching) of surface atoms or -moleculeswithout support from adsorbed atoms or molecules.

It can be assumed that the ion dives, in the range of 0<z<d, into theelectron density of the surface which decays exponentially into thevacuum, so that the electronic screening of the surface atoms as well asof the ion core become reduced. This results in a repulsive Coulombforce between the ion core and all nearby surface atoms, or all nearbyadsorbed atoms, respectively. For Ar⁺ ions at a distance of 1.0 a₀ infront of the surface atom-, or adsorbed atom nuclei, respectively, thisrepulsive potential reaches values of the order of 20 eV (for Mg) up to116 eV (for Pt), that is on the average about 65±45 eV for all surfaceelements from the lowest to the highest atomic number andcorrespondingly higher values for higher charged Ar-ions with effectivecharge >1. Depending on its effective charge q_(eff) in this spatialregion in front of the surface an initially highly charged ion will betotally reflected if its initial kinetic energy amounts to E₀ <(65±45)·qeV. Since q_(eff) is unknown as yet, the lowest possible kineticenergies of the highly charged ions are required in order to guarantee atotal reflection of the ions at the surface. To obtain total reflectionat the collective surface potential, is essential for the invention,since practically no surface atom can be expelled from the material'ssurface by transfer of kinetic energy in a collision between the ion anda single surface atom. The reduction of the rate of sputtering whenlowering the kinetic energy of singly charged ions has definitely beendemonstrated (H. Gnaser and H. Oechsner, Surface Science 251/252, 1991,pages 696 to 700; see also J. Muri and Ch. Steinbruchel, II, pages 41 to46).

At electrically conducting surfaces one has to subtract another energyE_(B) from the defined limit of energy E₀ which results from theacceleration of the ions by the image charge. It is composed of twoterms which geometrically correspond to the regions z>z_(c) andz_(c) >z>d, respectively. In the first region one has to use the initialcharge q of the ion, yielding a gain of energy E_(B1) =27.2·q/z_(c) eVup to the distance z_(c) from the surface. In the second region, theeffective charge of the ion is unknown, so that only a rough estimate ispossible. Under the assumption of limited screening by highly excitedelectrons in the essentially neutralized atom, one may adopt q_(eff)-q/2 and so obtains E_(B2) -27.2·(q/2)·(d⁻¹ -z_(c) ⁻¹) eV. As limitingenergy for total reflection one thus obtains on the average E₀(65±45)·(q/2)-E_(B1) -E_(B2), which corresponds to approximately E₀-(29±23)·q eV. Depending on the surface material one therefore has tochoose the limiting initial energy of the highly charged ions below 6·qand 52·q eV in order to guarantee the total reflection of the ions atthe surface and thus a negligible sputtering by the ions, that is atreatment of the surface with little damage.

Depending on the surface material and on the choice of E₀, distances ofclosest approach z₀ between surface atoms or -molecules and the ionduring the total reflection are expected to range from 0.5 to 2.0 a₀.These are distances at which the initially highly charged, but on itspath from z_(c) to z₀ neutralized ions, with the captured electrons inexternal shells, can capture electrons directly from filled inner shellsof the surface atoms or -molecules into its own, still partially emptyinner shells. Quasi-resonant electron exchange processes or inter-atomicAuger neutralization processes are responsible for this electroncapture, which takes place with a probability close to 1 for eachparticular ion at the turning point of its trajectory when it comesclose enough to a surface atom or to an atom or molecule adsorbed at thesurface.

This creates a very strong physical excitation of the surface atoms orof the atoms or molecules adsorbed at the surface, which results, due tothe loss of electrons, in a strong Coulomb repulsion and therefore inthe desorption of the atom in question, or, if the potential energydeposited is not sufficient for it, is transformed into an extremelylocalized thermal and chemical activation. This condition of a minimumapproach towards the atoms to be activated is as important for theclaimed process as the condition of total reflection.

The very low energy of the incoming ions has therefore not only to beselected following the criterion of total reflection, but has to beadapted such that the ions can come close enough to the surface atoms orto the atoms or molecules adsorbed at the surface, where close isdefined by the diameter of the orbits of the inner shell electrons to becaptured. The resulting optimized ion energies will thus depend on theion species and on the material to be physico-chemically activated, sothat theoretical estimates as well as experimental determinations willbe required from case to case.

It is essential for the invention that every low energy, initiallyhighly charged ion extracts, in the range of some nanometers in front ofthe surface, many valence electrons and, at the turning point of itstrajectory at the surface, at least one if not several inner shellelectrons from a surface atom or -molecule or from an adsorbed atom or-molecule. A high physico-chemical activation is so obtained with aspatial accuracy of a few nanometers for coating or etching, and aparticularly high activation is so created with a spatial accuracy ofsub-nanometers which especially supports the etching by additionaldesorption. With respect to the deposition of kinetic energy, whichextends over some tens to thousand nanometers due to the deceleration ofenergetic, singly charged ions, the energy deposition with highlycharged ions, with low kinetic but high potential energy is very welllocalized and allows therefore the coating or etching with spatialresolutions of the order of nanometers. This is a decisive advantage ofthe claimed process.

If the spatial resolution or anisotropy of the coating or etching is notrequired, it can be taken advantage of the great cross section forelectron capture of 10⁻¹⁴ to 10⁻¹⁵ cm² from free atoms or molecules,which are situated at a distance ≧5 nm from the surface, into highlycharged ions. The atoms are ionized and the molecules are divided intopartially ionized radicals by this electron loss, so that very reactiveparticles for coating and etching are produced. In order to producethese reaction partners in the close vicinity of the surface, it has tobe assured that the gases, gas mixtures, or vapors stream towards thesurface at low pressure (about 1 Pa) in a layer of only a fewmillimeters, since the average free path of highly charged ions amountsthen only to a few millimeters. Simultaneously it has to be consideredthat the ion trajectory up to this gas layer has to experience a vacuumof better than 10⁻² Pa, so that the ion penetrates this gas layer stillin its high charge state. When these differential pumping conditions aremet, large scale coating or etching with coat or etch rates of several100 nm s⁻¹ at ion current densities of several q·mA·cm⁻² can be achieveddue to the creation of several reactive radicals by each ion, where q isthe charge if the incoming ions.

If, however, high spatial resolution or anisotropy of the coating oretching is required, the production of reactants from the gaseous fluidat distances greater than the required resolution from the surface hasto avoided. This becomes possible by the particularly efficientphysico-chemical activation of atoms or molecules adsorbed or condensedat the surface. Adapting the rate of activation by a corresponding ioncurrent density of about q mA·cm-2 of highly charged ions to the rate ofadsorption of the gases, gas mixtures, or vapors, one can obtain vacuumconditions at which the ions arrive with a probability near 1 with theirinitial charge in the close vicinity of the surface (<3 nm) and activatethere coating or etching at rates of about 30 nm per second. The claimedprocess is particularly advantageous for the adsorption or condensationof the gases, gas mixtures, or vapors, since it can be applied at alltemperatures of the substrate. It leads therefore especially at lowtemperatures of the substrate (e.g. -100° C.) to very good results ofcoating or etching, since the totally reflected ion beam does not createa thermal load of the coating or of the surface material. Theadvantageous vacuum conditions can be further improved by applyingpulsed gas-, gas mixture-, or vapor beams, so that precise ion opticalimaging systems can be applied without being afraid of the scattering ofthe ions at gas particles. Highly charged ions of strongly reactivegases can so be applied for an etching process, so that a minimum ofadditional fluid is required; for the borderline case one may etch evenwithout additional fluid.

In addition to the above, the invention is further characterized by thefollowing features:

The advantageous vacuum conditions can be further improved by applyingpulsed gas-, gas mixture-, or vapor beams, so that precise ion opticalimaging systems can be introduced without being afraid of the scatteringof the ions at gas particles.

Since highly charged ions of low kinetic energy can also be used for thecleaning and smoothing of surfaces, one can apply in the same vacuumvessel many successive steps of processing of the surface modificationfrom the first cleaning of the surface of the substrate up to the verycomplex structuring on the nanometer scale by using precise ion opticalimaging and corresponding variable gas dosage, and can so obtain a highproductivity.

In summary one can conclude, that the advantages of the invention aremainly based on the fact that the coating and etching of surfaces withlittle damage results mainly from the potential energy stored in highlycharged ions, in contrast to the use of the kinetic energy of singlycharged ions in processes applied thus far. The invention described willimprove the productivity in all production processes, where RIE-, RIBE,PECVD-, or IACVD-processes are used, by reduction of the rejects due todamage, which will largely compensate the higher investments necessaryfor the claimed process. The invention quoted in the claims will producea significant improvement of the precision of the spatially resolved andanisotropic coating and etching, which will allow a deeper etching andhigher coating at simultaneously greater structural density, so thatcompletely new technologies and areas of production will emerge. In allproduction processes, which had to work without the application of RIE-,RIBE-, PECVD-, or IACVD-processes for reasons of costs, the process ofthe invention can reduce the costs by improving the quality and thus byreducing the rejects to such an extend, that it will impose itself inthe fabrication of micro- and nano-structures.

When working on electrically semi-conducting to non-conducting surfacesof substrates, the charging of the surface by the incoming positivelycharged ions can be compensated by simultaneous or intermittent spraysof electrons with low kinetic energy.

A further explanation of the invention follows with examples and anexplanation of the embodiments shown in the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a first arrangement or embodiment withwhich a modification of a surface by coating or etching can beperformed.

FIG. 2 is a schematic diagram of a second embodiment.

FIGS. 3 and 4 are schematic diagrams of further embodiments.

FIGS. 5 and 6 are schematic diagrams showing a specialization of thefirst two embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

(see FIG. 1)

FIG. 1 shows a schematic presentation of a first arrangement of a deviceto carry out the process, as it can be set up with nowadays technology.The figure of reference 1 shows an ion source with a modest vacuum (10⁻²Pa). CH₄ is fed into this ion source and transformed into a plasma 1'with variously charged C-atoms.

In the ion source 1 with the plasma 1' various C-ions are produced withan average charge q_(m) ≈+5. The exit aperture of the ion source is at apotential U below +10 and about +60 V. With an extraction electrode 2and an electrostatic extraction lens 3, both on a potential of (e.g.)-20 kV, ions with a mixture of charge states are extracted and areaccelerated to (20000+U)·q eV into a zone of pressure of 10⁻⁵ Pa. Theextraction lens 3 focuses these ions through entrance aperture 5 into adouble focusing sector-magnet 6 or into an ion optical device forq/m-separation, so that ions with a single charge state, here e.g. C⁵⁺,are focused through the exit aperture 7.

This exit aperture serves simultaneously as differential pumpingdiaphragm, through which the ions enter into a zone of pressure of about10⁻⁷ Pa. There the ions are decelerated by a first deceleration lens 9from (20000+U)·q eV to e.g. (1000+U)·q eV and are focused through asecond differential pumping diaphragm 10. This allows the set up of asecond deceleration lens 11 and the positioning of a surface to becoated 12 in an ultra-high vacuum of about 10⁻⁹ Pa. The ions, selectedwith respect to their q/m, are decelerated in the deceleration lens 11from (1000+U)·q eV to U eV and hit the surface 12 with low energy, whichin this case is a silicon single crystal substrate (wafer) for the chipproduction. For the thermal conditioning of the surface 12 a heating 13and/or a cooling device 14 are provided. A (schematically indicated)orientation device 21 is provided in order to adjust various angles ofimpact on the substrate 20. The feeding of the gas, gas mixture, orvapor is provided in this example through nozzles 15, which are arrangedsymmetrically around the ion beam axis, in order to achieve ahomogeneous stream of gas 19 onto the surface hit by the ion beam 22.

Valves 24 (e.g. piezo-ceramic valves) are provided just in front of thenozzles 15 which allow a pulsing of the gas stream. In this example amixture of CH₄ and H₂ is used to produce a diamond coating of thesilicon single crystal. Diamond is a metastable form of carbon. For itsformation it requires an additional activation energy which is suppliedby the C⁵⁺ -ions. The potential energy of the ion produces at impact ina very short time a very localized (<some nm²) electronic and thermalactivation, which may be understood as high local temperature. Thecarbon is transformed by this high, local electronic and thermalactivation in the presence of H-atoms into the desired diamondstructure. The subsequent very rapid decay of the local electronic andthermal activation stabilizes the diamond structure.

EXAMPLE 2

(see FIG. 1)

Alternatively, the production of a molecular beam of the desiredmaterial by sputtering with a Ar⁺ -ion beam 16 of about 1 to 5 keVkinetic energy is shown in FIG. 1. The ion beam is produced in a Ar-ionsource 17 and is directed onto the material to be sputtered 18 right infront of the surface 12 to be coated. The material to be sputtered 18 ise.g. solid boron, which as a consequence of the sputtering with theAr-ions hits a metal surface 12 as B- atomic- and B₂ - molecular beam.At the metal surface it interacts with a beam 22 of low energy, highlycharged nitrogen ions for the production of a coating of boron nitride(BN). In order to obtain a still better homogeneity of the coating,rotations and linear displacements of the substrate 20 with its surface12 are provided by a schematically shown orientation device 21.Depending on the application other vacuum conditions and otherconditions of acceleration and deceleration can be used.

EXAMPLE 3

(see FIG. 2)

Example 3 corresponds to example 1 with respect to essential details,except for the omission of the q/m separating unit.

SiH₄ streams into the ion source 1 and is dissociated into ions. Thewhole mixture of charge states of Si ions, as extracted from the plasma1' of the ions source 1, hit the surface 12, which here is a SiO₂ -filmon a wafer, with an energy U·q eV. This increases the total stream ofparticles onto the surface 12 and therefore also the coating power, butdecreases on the average the physico-chemical activation, since, besidesthe highly charged ions, a high fraction of only singly and doublycharged ions will be present in the stream of particles. These ionscontribute less to the physico-chemical activation than the highlycharged ones. It is therefore important to use ion sources which canproduce streams of particles with an optimum average charge state. Theoptimum is defined economically and technologically, since thetechnological effort of the construction of the ion source can beadapted to the lowest charge state of an ionized element with whichefficient coating powers can be obtained corresponding to the invention.

The feeding of gas is provided in this example by a perforated matrix ofnozzles 25, through which a mixture of SiH₄ and N₂ streams ashomogeneously as possible onto the SiO₂ -film on the surface 12, where aSi₃ N₄ -coating is deposited in interaction with the Si-ions. Since theion beam 23 is focused in this example through the hole in thenozzle-matrix 25, the substrate 20 with the surface 12 can be movedmulti-parametrically with the device 21, in order to allow either for ahomogeneous large scale coating or for coating inscription with Si₃ N₄on the SiO₂ -film. For the optimum temperature for this coating of thesurface a heating 13 and/or a cooling device 14 have to be provided,using one of the known systems. Depending on the application othervacuum conditions and other conditions of acceleration and decelerationcan be used.

EXAMPLES 4

Example 4 corresponds to example 1 with respect to essential details,except for the fact that the whole set up from the ion source up to thesurface to be treated is built in ultra-high vacuum technology (10⁻⁹Pa). In this way the greatest cleanness of the apparatus becomespossible at vacuum conditions at choice. At corresponding operation ofthe ion source the differential pumping diaphragms 7 and 10 can then beeliminated.

EXAMPLES 5

Example 5 corresponds to example 3 with respect to essential details,except for the fact that the whole set up from the ion source up to thesurface to be treated is built in ultra-high vacuum technology (10⁻⁹Pa). In this way the greatest cleanness of the apparatus becomespossible at vacuum conditions at choice. At corresponding operation ofthe ion source the differential pumping diaphragms 7 and 10 can then beeliminated.

EXAMPLE 6

(see FIG. 3)

A mixture of charge states 30 is extracted as stream of particles, hereof fluorine ions, from an ion source 1 with U·q eV directly in thedirection onto the surface 12, here a Si single crystal, where theextraction voltage is ≈+1 V<U<≠+60 V. In comparison to example 1 noq/m-separation and no ion-optical imaging takes place; the differentialpumping stages are also eliminated. As in FIG. 1 valves 37 can beprovided, however, to pulse the molecular beam.

The total stream of particles onto the surface 12 and therefore theetching power are increased, but the physico-chemical activation isdecreased on the average, since, depending on the ion source, besidesthe highly charged ions, a high fraction of only singly and doublycharged ions will be present in the stream of particles 30 whichcontribute less to the activation than the highly charged ones. It istherefore important to use ion sources which can produce streams ofparticles with an optimum average charge state. As mentioned already,the optimum is defined economically and technologically. The magneticfield distribution is shown in the diagram in the lower part of FIG. 3.

Since sources for highly charged ions mostly work with high magneticfield confinement of the ions and electrons, this example can only beapplied in situations where magnetic stray fields do not disturb thefurther treatment of the surface. The gas feeding is provided in thisexample in the form of molecular beams 36, which are defined by nozzles31, apertures 32 and differential pumpings 35. In this way a veryhomogeneous stream, of SiF₄ e.g., onto the surface is achieved, in orderto imprint, due to the interaction with the Si-ions, a precise etchingpattern into the Si-surface through a mask which had been deposited bylithographic methods onto the surface. The Si-surface can be movedmulti-parametrically with the device 21, in order to achieve a stillbetter large scale homogeneity of the etching or obtain particular etchprofiles. For the optimum temperature for this etching a heating 13and/or a cooling device 14 have to be provided, using one of the knownprocesses. Depending on the application other vacuum conditions andother conditions of acceleration and deceleration, e.g. by a differentdistribution of the magnetic field strength, can be used.

EXAMPLE 7

(see FIG. 4)

The total mixture of charge states of a plasma, here a chlorine plasma,is accelerated with U·q eV, where +1 V<U<≈+60 V, directly onto thesurface 12, here a substrate 20 with an Al₂ O₃ -surface, which is a wallof the plasma volume 1. The vacuum conditions can be adapted to theparticular application. With respect to the example 6 a furthersimplification has thus been introduced. All further explanations of theexample 6 are to be applied to example 7 as well. As in the example 6 itis important to use a configuration of the plasma production (plasma 1')which ensures a content of optimum average charge state. The optimum isdefined here economically and technologically. This example resemblesvery much the technical setup of the known plasma-etching according theECR-principle, where a plasma with low average charge state is mixedwith chemical substances in order to erode surfaces via plasma enhancedchemical reactions (see I, chapter 5, pages 138 to 157).

The decisive difference of example 7 is the use of a plasma with highaverage charge state (q_(m) >>2), which may also be produced by theECR-principle, but requires a high magnetic plasma confinement, as itnot used for the plasma etching as yet. The FIG. 4 explicitly shows oneof many possible arrangements according to the ECR-principle with highmagnetic plasma confinement, with axial plasma confinement in an axialmagnetic field, the relative strength of which is indicated, and with aradial plasma confinement by an as high as possible magnetic multipolarfield.

The gas feeding, CCl₄ e.g., is provided in this example by effusion fromnozzles 15 which are arranged symmetrically around the axis and whichproduce in the region of the surface an increased density of CCl₄. Bythe interaction with the Cl-ions a precise etching pattern can so beimprinted on the Al₂ O₃ -surface through a mask, produced bylithographic methods on the Al₂ O₃ -surface. The Al₂ O₃ -surface can berotated in order to produce certain etch-profiles by means of theCl-ions, which move predominantly parallel to the axis of the system.The motion of the ions parallel to the axis of the system is enhanced bythe presence of the homogeneous magnetic field in the region of thesurface. For the optimum temperature for this etching a heating 13and/or a cooling device 14 have to be provided, using one of the knownprocesses. Depending on the application other vacuum conditions andother conditions of acceleration and deceleration can be used.

EXAMPLE 8

(see FIG. 5)

The example 8 is based on the examples 1-5 and uses just in front of thesurface 12 ion optical elements, which allow a sharp focusing of the ionbeam, here e.g. Ti-ions, and a controlled electromagnetic guidance ofthis focus on the surface. They may also allow a sharp imaging of asemi- transparent mask on the surface 12, here e.g. a metal. With thismethod a TiN-coating pattern can be imprinted on the surface by feedingN₂ -gas through the nozzles 15 for instance. Since many arrangementsexist for the electromagnetic guidance of a ion beam focus and for theimaging of a semi-transparent mask on the surface, only one possibilityis shown in FIG. 5. In the device in FIG. 5 a differential pumpingdiaphragm 10 is set up as aperture with very small and variable radius,which is imaged with ion optical components 40 on a very sharp focus 41.In the direction of the ion beam behind this aperture an electromagneticdeflection system 42 is provided which allows the controlled guidance ofthe focus 41 on the surface 12.

EXAMPLE 9

(see FIG. 6)

A further arrangement is shown in FIG. 6 which illuminates thesemi-transparent mask 45 parallel to the axis by a first set of ionoptical components 46, and then images this mask 45 with a second set ofion optical components with a good focus on the surface. By means ofthis mask an etching pattern may be imprinted on a Pt-surface by usingCBrF₃ -gas and low energy, highly charged F-ions.

There has thus been shown and described a novel process and device forsurface-modification by physicochemical reactions of gases or vapors onsurfaces, using highly-charged ions which fulfills all the objects andadvantages sought therefor. Many changes, modifications, variations andother uses and applications of the subject invention will, however,become apparent to those skilled in the art after considering thisspecification and the accompanying drawings which disclose the preferredembodiments thereof. All such changes, modifications, variations andother uses and applications which do not depart from the spirit andscope of the invention are deemed to be covered by the invention, whichis to be limited only by the claims which follow.

I claim:
 1. In a process for surface modification by physico-chemicalreactions, said process comprising the steps of:(a) contacting a solidsurface having a crystalline or amorphous structure with a reactive,gaseous fluid which is to interact with the surface; and (b) supplyingactivating energy to both said fluid and said surface by means of ionsor plasmas, in order to trigger reactions between said fluid and saidsurface, the improvement comprising providing an activating energy inthe form of an electronic potential energy of ions having a charge ofq≧2 with a low kinetic energy, or by streams of plasmas, which contain ahigh proportion of an arithmetically averaged charge state Σq·ƒ(g)=qm≧2, where ƒ(g) is a fraction of particles in charge state q=0,1,2, . . ., with said low kinetic energy, wherein said low kinetic energy is belowabout 100·q eV and determined to meet a condition that said ions areallowed to closely approach atoms of said surface, but not to penetratesaid surface.
 2. The process according to claim 1, wherein the surfacemodification comprises an etching process.
 3. The process according toclaim 1, wherein the surface modification comprises a coating process.4. The process according to claim 1, wherein the surface modificationcomprises a deposition process.
 5. The process according to claim 1,wherein said fluid is provided as spatially homogeneous atomic ormolecular ion beams directed toward said surface at an arbitrarilyselected angle in a vacuum between about 10⁻² and 10⁻⁹ Pa such that saidlow kinetic energy, ions are injected from a region of said vacuumtraverse a limited region of gas, and then impinge said surface.
 6. Theprocess according to claim 1, wherein the surface modification isconducted at a surface temperature below 600° C.
 7. The processaccording to claim 1, wherein one or several mono-layers of said fluidare adsorbed at said surface and are physicochemically activated by saidlow kinetic energy ions.
 8. The process according to claim 1, whereinfurther comprising the step of adsorbing a portion of said fluid at saidsurface by either:(i) providing said low kinetic energy ions as acontinuous ion beam and supplying said fluid in the form of pulses ofdefined quantity corresponding to one to three mono-layers of saidadsorbed fluid at said surface or (ii) providing said low kinetic energyions as intermittent pulses of ions and supplying fluid pulses of saidfluid having defined quantity of said fluid corresponding to one tothree mono-layers of adsorbed fluid, a quantity of an ion pulse beingadapted to a necessary activating energy of said adsorbed mono-layers aflux and an adsorption of said fluid at said surface being adapted tosaid continuous ion beam or said ion pulses such that said ionsstatistically interact with a fresh mono-layer of said adsorbed fluid.9. The process according to claim 1, wherein said fluid is produced bysputtering a solid material with ions having a sufficient kinetic energyto cause said sputtering.
 10. The process according to claim 9, whereinsaid solid material is boron.
 11. The process according to claim 1,wherein said process of surface modification is started with a stream ofhighly charged ions, having a high kinetic energy sufficient topenetrate said surface, directed at said surface which is subsequentlychanged to a stream of said low kinetic energy ions whereby said highkinetic energy ions penetrate into said surface at the beginning of theetching process, or to improve adhesion at the beginning of a coatingprocess by the linking to crystalline defects.
 12. The process accordingto claim 1, wherein said activating energy is provided as a stream ofsaid ions of an element which represents a significant constituent ofsaid surface to be modified.
 13. The process according to claim 1,wherein said highly charged ions are:produced in an ion source;extracted, and optionally separated with respect to a charge to massratio (q/m); transported to a processing chamber; and decelerated tosaid low kinetic energy per charge in front of said surface to bemodified.
 14. The process according to claim 1, wherein an angle ofincidence, a position of impact, and a size of an impact spot of saidions on said surface to be modified are controlled.
 15. The processaccording to claim 1, wherein said ions are produced in a region withmagnetic plasma confinement by feeding energy via electron beams or viamicrowaves employing electron cyclotron resonance, and wherein theplasma with low kinetic energy ions is brought into direct contact withsaid surface to be modified.
 16. The process according to claim 1,wherein one or more devices selected from the group consisting of anelectron-cyclotron-resonance ion source with magnetic plasmaconfinement, an electron impact ion source, and an electron beam ionsource is used to produce said ions.
 17. The process according to claim1, wherein said highly charged ions irradiates a perforated mask whichis imaged onto said surface, such that an etched or coated image of saidmask is produced on said surface.
 18. The process according to claimwherein said fluid homogeneously streams out of a matrix of nozzles onto said surface, and wherein said low kinetic energy ions are injectedfrom a region of vacuum sufficient to impinge said surface and impingesaid surface through holes in said matrix of nozzles.
 19. The processaccording to claim 1, wherein the reactions take place at a surfacetemperature of below 0° C.
 20. The process according to claim 1, whereinsaid kinetic energy of said ions is between about 1·q eV and 60·q eV.